In general, for an oscillating type actuator (hereafter “actuator”) which makes reciprocating rotational movement (“center-of-a-circle swing”) in a predetermined rotation angle range, a stator and a moving element are installed in a housing. The stator is equipped with a magnet coil which makes circuitry connection to a reciprocal transformation means of a electric current direction, and the moving element is equipped with a permanent magnet. The circular reciprocating movement (“center-of-a-circle swing”) is carried out for the moving element within the limit of a predetermined central angle by changing directions of a magnetic field (or magnetic flux) by the change of the energizing direction to the aforementioned magnet coil, and by producing the magnetic propulsion force of attraction and repulsion between the magnet coil and the permanent magnet.
Such an actuator is widely used as a power source in various industrial equipment. For example, it is used as a driving means of a flap for changing paper feeding directions, such as in ATM (automatic teller's machine) and a printer.
This type of flap is more often being stopped at one of the end sides (beginning/ending points or a reversing position of a swing) rather than being constantly and continuously swung. As to the stopping method, there is a method that the permanent magnet and the magnet coil are attracted with one another by energizing the magnet coil by supplying electric current (energization holding). There is another method that a core (magnetic material) of the magnet coil and the permanent magnet are attracted with one another by not supplying the electric current (non-energization holding).
However, the actuator of the energization holding method is not preferable in view of recent trend in power saving and energy consumption reduction. Thus, the actuator of the non-energization holding method is preferable, especially when a standby time of ATM is long.
To respond to such needs, inventions are disclosed, for example, in Patent document 1, Patent document 2, and Patent document 3.
First, the invention disclosed in Patent document 1 relates to that shown in a prior application by the present applicant. One of the objects of the invention relates to a holding force at the time of non-energization holding like the present application.
According to the representative drawing of the prior application shown in FIG. 9, it comprises a single magnet coil (3) in a case (2), an oscillating arm (5) that is held to the shaft supported pivotally to be rotatable in the case (2), and two permanent magnets arranged in parallel with different polarities via a predetermined air gap to the magnet coil (3) and equipped to the oscillating arm (5). By this configuration, the center-of-a-circle swing is carried out due to the attraction and repulsion of magnetic forces between the energized magnetic coil (3) and the permanent magnets (7) of the oscillating arm (5) within the range prescribed by a stopper (8). This swinging force is output to the outside as a power source from an output shaft (4). In the oscillating arm (5) holding the permanent magnet (7), a back yoke (6) made of magnetic material is arranged to the counter side of the magnet coil (3), thereby controlling the magnetic flux direction of the permanent magnet (7) and strengthening magnetic force. Due to this configuration, stable holding is achieved at the position where the oscillating arm (5) is restricted by the stopper (8) due to the magnetic attraction by the residual magnetic flux of a magnetic core (31) of the non-energized magnet coil (3) and the permanent magnet (7).
Next, according to the representative drawing of the gazette attachment which is reproduced in FIG. 10, the invention disclosed in Patent document 2 has a swinging coil holder (14) which is held by a shaft (12) in a manner to swing around and constituted from a moving coil (16). A permanent magnet (17) for a latch is provided to the outside end of the swinging direction of that coil holder (14), and a magnetic material is provided in a case wall as a stopper to prescribe a swing distance for this latch magnet. By this configuration, the holding force at the non-energized time is secured by magnetic attraction between the aforementioned permanent magnet for the latch (17) and the magnetic stopper.
The invention disclosed in Patent document 3 is considered to be made based on the invention disclosed by above-mentioned Patent document 1. According to the gazette accompanying drawing which is reproduced in FIG. 11, a swing yoke (50) to which two magnets (51, 52) are fixed side by side, and a fixed yoke (30) having protruding parts (31, 32) at its sides are provided. By providing a magnet coil (43) having a main pole (41) at around the center of the fixed yoke (30), a minimum distance magnetic circuit is formed from one of the magnets (51 or 52) to a main pole (41), the fixed yoke (30), the protruding parts (31, 32), and to the other one of the magnets (52 or 51). It aims to attain the characteristic equal to or greater than the conventional technology even when the grade (residual magnetic flux density, etc.) of the magnet (for example, bond magnet, etc.) is low.